The present invention relates to a system and method for active cooling of a computer microprocessor (CPU) to reduce the heat problems.
Processor power, and therefore speed, is increasing rapidly. From the beginning of personal computers and until now, the trend of increasing temperature in CPUs is clear.
The first processor models, such as XT, 286, 386 did not require any thermal solutions. Their power consumption and, therefore, temperature was low. When the 486 came out, it needed a small heat sink (an aluminum plate attached to the CPU) to decrease and remove the heat. The heat is increased due to the increasing number of transistors, also called CMOS devices, located on the silicon wafer, and increasing switching speed. Each CPU model has several versions of switching speed, and the switching speed and temperature are correlated.
The Pentium CPU needs a heat sink and a fan. Thus, a whole new market of passive cooling solutions emerged. Pentium II models came out with a different structure, with increasing power and heat. This CPU, and others such as the AMD Athlon or Thunderbird CPU model, for example, needed a very large heat sink and fan, and sometimes two fans or more (Pentium 4). The trend of rising heat continued.
The heat of a CPU reduces its reliability, and therefore the reliability of the entire computer system, and affects the switching speed. Therefore, it is crucial for the efficient performance and operation of the computer system to reduce the heat of the CPU.
As more and more transistors are placed on a small silicon wafer, and switching speed increases, the chip temperature increases on the silicon chip, creating a very small area of high heat that must be removed quickly and efficiently. While chip manufacturers are interested in keeping chip size small, so as to make more chips from a single silicon wafer, keeping the chip size small while increasing power, speed and number of transistors is problematic. Furthermore, the chip sensitivity increases as the size of transistors inside the chip decreases and the number of transistors increases. Thus, a rapid change in temperature, such as when turning the computer on or off, can lead to a short life, errors, and total failure of the chip.
Passive solutions cannot pump heat in an efficient way from a small spot producing a great deal of heat (the efficiency above 50 W decreases fast), although some efforts were made in the direction of using other materials, such as copper heat sinks and better attachment material between the silicon chip and the heat sink (such as phase change interface pad from Chomerics (Parker Hannifin Corp, 77 Dragon Court, Woburn, Mass. 01888-4014, U.S.A) that reduces the thermal resistance, or Arctic cool by Agilent (Palo Alto, Calif., U.S.A.). These improvements are all passive, and not able sufficiently to reduce, heat pump, and control the temperature, as can an active cooling system.
It will be appreciated that the important parameters are the amount of heat pumped (in Watts), and the temperature decrease (delta T in degrees Celsius). Both of these parameters are important, as each CPU has an absolute maximum temperature defined by the manufacturer (maximum T case). For example, Pentium 4 run at 1.5 GHz, maximum temperature of 72xc2x0 C. (See xe2x80x9cIntel thermal specificationxe2x80x9d, section 6.1, from Intel Pentium 4 data sheet). The heat pump, defined in watts, must, therefore, pump sufficient heat to maintain the CPU inside the permitted range, with an acceptable safety margin.
Some passive coolers are better then others and while they can improve heat pump power, the temperature often rises to dangerous level.
Another way to solve this problem is to increase the chip size. However, from a business point of view, in doing so as, from a single silicon wafer, they will be able to produce fewer chips, which means increased cost and creating a manufacturing capacity problem.
A further problem of high speed CPU""s is that, when the computer is turned off or in the case of a power cut, fast changing temperature over a short period of time often results in thermal shock, which could change characteristics of the CPU and reduce reliability. Another problem which arises when switching the unit off is that the fast rise in temperature can cause cooling liquid condensation in the unit""s cold side, which can lead to serious problems.
The conventional cooling systems described above are all passive systems. This means that they remove heat from the CPU of the computer system by means of passive components, such as fans and heat sinks, but do not actively input cold by pumping the heat with active components, to accelerate heat pumping, delta T, and efficiency. The passive solutions cannot control the temperature, as they are passive and do not utilize electronic control. In addition, the reaction time and heat pumping over time is very low, compared to active cooling. For example, low reaction time when turning on the computer can cause a fast change in temperature inside the chip over a very short period of time, causing thermal shock to the chip that can cause damage.
At present, passive cooling solutions are close to their limit. A new solution and approach are needed. Active cooling can pump out a high power of heat and reduce chip temperature. Decreasing the CPU temperature will allow increasing the switching speed. These phenomena are known as thermal acceleration.
A computer including an active cooling system has been proposed by KryoTech, Inc., of West Colombia, S.C., USA. This computer utilizes a vapor phase cooling method, and includes a compressor and condenser with gas and moving mechanical parts mounted inside a special, custom-made PC case. KryoTech markets an accelerated speed computer, and does not provide a generic solution.
Also Kryotech requires a special turn-off procedure to avoid thermal shock and condensation. This procedure must be followed by a human user, which can lead to mistakes and damage. Furthermore, when using the Kryotech system, the user must use an expensive UPS (Uninterruptible Power Supply).
Thermo Electric Cooler (TEC) components, components based on the Paltier effect, are well known in the relevant industry. When electrical DC power is supplied to the TEC component, one side of the component becomes very cold and the other side very hot (partly because of heat pulled from the CPU itself, and partly due to the low efficiency of the TEC component which generates additional heat). In operation, the component actually pumps heat from the cold side to the hot side. The Thermo Electric Cooling component has a low efficiency, and demands high power for operation, which is one of the reasons TEC""s were generally not considered to be useful for cooling CPU""s and other heat producing components. There are many models of thermo electric coolers, each with different characteristics and requiring a different power input. For an advanced CPU, a high power thermo electric component is needed.
In addition to the problems discussed above regarding passive cooling systems, one problem encountered in cooling computer CPU""s by means of a TEC module is that the heat built up on the hot side of a thermoelectric module used for cooling must be removed from the PC box. (When applying cooling to the CPU, the hot side of the thermoelectric component is much hotter because of its low efficiency, around 30 percent).
The present invention, described below, is a complete system that solves all the problems mentioned above. In particular, it is a generic device, which can be mounted in any PC. As the system of the current invention is active, both the amount of heat pumped, and the temperature decrease can be achieved with significant improvement, as compared with conventional cooling systems.
There is provided, in accordance with the present invention, a cooling system for a heat sensitive element in an enclosure, such as a CPU, the cooling system including a high power active cooling unit having at least one Thermo Electric Cooler (TEC) component having a cooling liquid circuit passing through a cold side heat sink therein, the cooling liquid circuit being coupled to a heat sink coupled to the heat sensitive element and having a cooling liquid circuit therethrough; a dedicated power supply; and a controller for controlling the TEC components and the cooling liquid pump.
Preferably, the cooling liquid circuit includes water or a cooling liquid. According to one embodiment, the cooling liquid includes water mixed with ethyl glycol, to prevent corrosion when aluminum or copper parts are used in the system.
According to a preferred embodiment, the cooling system includes a plurality of TEC components, a single cooling liquid circuit passing through all the TEC components, and a cooling liquid pump
According to a preferred embodiment of the invention, the system of the present invention is configured as a PC enclosure cover. This embodiment will allow the use of active cooling for any PC or computer merely by making small changes in the pc/computer cover only.
There is also provided, accordance with the present invention, a method of cooling a heat sensitive element, such as a CPU, mounted in an enclosure, the method including coupling a high power active cooling unit energized by a dedicated power supply having at least one Thermo Electric Cooler (TEC) component to the enclosure, the TEC component having a cooling liquid circuit passing through a cold side heat sink therein; and coupling the cooling liquid circuit to a cooling liquid circuit in a heat sink coupled to the heat sensitive element.
According to a preferred embodiment, the high power active cooling unit includes a plurality of TEC components, a single cooling liquid circuit passing through all the TEC components, and a cooling liquid pump.